Typescript p-fileUpload多个文件上载错误

prime ng file upload htm代码，用于上载多个文件

 <div class="col-lg-12 col-md-12 col-sm-12">
      <p-fileUpload name="demo[]"   customUpload="true" (uploadHandler)="onUpload($event)" multiple="multiple" accept="image/*"
          maxFileSize="1000000">
          <ng-template pTemplate="content">
              <ul *ngIf="uploadedFiles">
                  <li *ngFor="let file of uploadedFiles">{{file.name}} - {{file.size}} bytes</li>
              </ul>
          </ng-template>
      </p-fileUpload>
  </div>

上载服务以调用实际的后端服务

upload(file: FormData): Observable<any> {

   const req = new HttpRequest('POST', CommonConstants.env+"api/master/upload", file, {
     responseType: 'json'
   });

   return this.http.request(req);

 }

上传（文件：FormData）：可观察{
const req=new HttpRequest（'POST'，CommonConstants.env+“api/master/upload”，文件{
responseType:'json'
});
返回这个.http.request（req）；
}

加载时返回错误“core.js:6014 error TypeError:无法读取未定义的属性“method” 位于HttpXhrBackend.handle（http.js:2325）”

upload(file: FormData): Observable<any> {

   const req = new HttpRequest('POST', CommonConstants.env+"api/master/upload", file, {
     responseType: 'json'
   });

   return this.http.request(req);

 }